1.21 Assume that C represents the average cost for n wells drilled to a mean depth, Di, and that C varies approximately exponentially with depth such that an expression Czaebb Can be used to curve fit N observed values of ni, Ci, and Di. if we define a residual error, ri, as r =n. In it is possible to determine the constants a and b using the N observed values of ni, Di, and Ci such that the sum of the residuals squares has a minimum value. Derive expressions for a and b that result in a minimum value of 1.22 Apply the expressions for a and b derived in Exercise 1.21 to obtain a least-square curve fit of the south Louisiana completed well cost data given in the table 1.7 for well depths below 7,500ft. 1.23 Complete the following using the cost vs. depth data given in table 1.7 for dry holes drilled in south Louisiana in 1978 a) A plot of cost vs. depth on Cartesian paper. b) A plot of cost vs. depth on semilog paper. c) Determine a set of constants a and b of Eq. 1.17 that allow a curve fit of these data. Aswer: $65.513 and 0.000212